Max Revs on a Cast Crank SBC?

[85 Cutlass Brougham]

I am curious about this. I have a cast crank 350 with cast pistons and a 2 bolt main block. The only bottom end modifications are a Z-28 style oil pump and ARP rod bolts. How high can this thing safely be revved? I have the limiter set at 6,000 RPM, but tend to shift it at 5500.

As a corollary to this, I am sort of mulling over the idea of a high RPM SBC for road racing right now. Not that I can afford to build it, but I wonder what I could do to build such a monster. I am thinking a 400 block with a 283 crank and spacer bearings, and 6.2+in rods. Add to it some lightweight pistons and a roller valvetrain and maybe dry sump oiling. Road racing is the idea with this one and low end torque would only need to be adequate, not exceptional as it would mainly be used from a rolling start and not for a standing quarter or eighth drag race.

 

[82355supreme]

Cast cranks will live on the street at 6-6500. Notice i said the street though. It's not seeing these rpms for any sustained amount of time.

It's the stock rods I'd worry about before the crank.

 

[85 Cutlass Brougham]

Well, this is all part of my desire to use the car as a bit of a track sl*t. I do worry about the whole bottom end of this thing as it was not originally intended to see much in the way of RPM's. I would like to build something that can take 7500-8000 RPM for when it sees track time (on a road course, not a drag strip), but I am debating building another car that is better suited to track duty instead of using this one too often (Probably a 240sx or AE-86 Corolla).

 

[gs dewd]

Well, this is all part of my desire to use the car as a bit of a track sl*t. I do worry about the whole bottom end of this thing as it was not originally intended to see much in the way of RPM's. I would like to build something that can take 7500-8000 RPM for when it sees track time (on a road course, not a drag strip), but I am debating building another car that is better suited to track duty instead of using this one too often (Probably a 240sx or AE-86 Corolla).

7500 to 8000 wow. You are going to need and I am guessing here a steel crank, forged pistons, h beam rods,and 4 bolt mains to live under sustained high rpms. Hell when I had my Eclipse gsx I had a complete built motor and was scared to hold the rpms past 6500 for to long even though I shifted at 8500. I would guess you may need to consult with someone who builds or races sm blk chevy's on a road course and see what they use.

 

[Doober]

Take a look here
http://maliburacing.com/forum/viewtopic.php?f=2&t=79673

 

[85 Cutlass Brougham]

I guess I am safe if I leave the limiter where it is then for this engine. It would need to be able to stay in the upper RPM's for extended time if I did decide to try to be competitive (Time Attacks, etc. ) with it. That is why I was thinking in terms of a short stroke/long rod engine. That would reduce piston speeds and loading on the cylinder walls. I know I can build a bottom end that would work, but I worry about the valvetrain. Pushrod valvetrains tend to have too much mass to rev as high as, say a DOHC design would. You can lighten it, but then you hit other issues like cost. Hmm...

 

[utfan01ss]

You sure are planning on twisting that thing for road racing aren't you! I hit around 6500 - 7000 RPM's with my LS1 on Road Atlanta occasionally but most of the time it's below those RPM's. Set your gearing up so your engine doesn't have to wind up so far to make peak power. 6500 on a SBC is plenty for road track duty, though I've never built a Gen 1 SBC for this purpose but I have some buddies that did. My friend Devin built a 355 which used the stock cast crank, Pink Rods with ARP rod bolts, Coated Hypereutectic pistons, AFR 200cc aluminum heads with dual springs, titanium retainers, full roller rockers, hardened pushrods, a comp roller cam, victor Jr. intake with a Demon carb and long tube headers. I don't know the specs on the cam but it makes peak power at 6200 RPM's and pulls like mad all the way to 6500 RPM's. This motor has been beat on for three years without any issues. Just be sure to use a windage tray to keep the oil in the pan, a high volume oil pump and drill out the oil return passages in the lifter valley so the bottom end won't get starved of oil at high RPM's. Those motors can take a beating if set up properly. My SS has Yella Terra roller rockers, AFR heads with dual springs, titanium retainers and hardened pushrods and it flat out screams in the top end. Granted a LS1 is a completely different engine than a SBC. Either way good luck and beat the hell out of it!

 

[85 Cutlass Brougham]

Well, I am not planning on revving this 350 too high, at least I hope I won't. It has a 3.23 gear in it right now, which is just about perfect to work the engine's power band according to the simulations I ran on the computer. On the sim, it has a very flat torque curve from 1800-5,000 RPM and never dips below 380 ft/lbs in that range, and maxes at 425 ft/lbs. Luckily, this means it really doesn't need much gear to get going, and any more gear would only make it easier to spin the tires without being any faster. I'll see how it goes I guess. I am going to try to get a competition license through either the SCCA or NASA, but I have to learn a lot about track driving first. If I really enjoy this, I will probably build a dedicated track car out of a lighter vehicle like an AE-86 Corolla or S-13 240sx. That's in the future though, so for now I guess I will upgrade the oil pan, do the 5 speed swap, and put good tires on it.

 

[rippinriley]

I have a 355 with flatop forged trw's ,cast crank ,x rods with arp bolts ,moroso deep pan with windage tray, an old wolverine blue racer hydruliac cam [510 lift intake & exhaust] sportsman 2 heads , mighty demon 750. That I built in 1998 & I twist it to 6,800 + rpm's all the time, I also spray 150 horse of nitrous on occasion. This is my old test mule that I run when I freshen my other motors. it runs 12.90's on the motor & 11.6's on the hose.I have tried to blow it up several times but it just keeps taking it. I guess sometimes you just get a good one?

 

[chevypower86olds]

ok , my friend has a 69 camaro with 12 bolt posi 4.11, 3500 stall, turbo 350 trans , me and him built a 355 sbc ...balanced with doug herbert 630 lift solid roller 106 lobe seperation, chevy cast crank, vortec powdered metal rods(pm) old school forged heavy pistons ,dart pro 1 heads ..2.05 valves. and believe it or not a 250hp nos kit on top of that!! just runs the nitrous down the track only. shifts at 7000-7200 rpm. best time was only 11.01 on a 1/4 pass at 125mph at atlanta dragway here in commerce. . not bad for a fully dressed everyday streetcar. missed drive a couple times in the past down the track..talking about over rev with the button mashed....8500 no problem. pm rods and cast crank lasted 3 years. never broke a stock cast crank! car was low on oil one night cutting doughnuts while shifting to second gear...slinging around so fast the 2 quart low of oil didnt pick up and rod come loose...did coast home to change it out the next night! cant say a small block chevy aint tough or cant take a beatin! the pm rods are well worth the insurance if your gonna run a cast crank. so 6,000 rpm is not a problem with a cast crank.